A chemically-amplified resist has been used in the field of microfabrication such as the production of integrated circuit devices. The chemically-amplified resist is designed so that an acid is generated in an area exposed to short-wavelength radiation (e.g., excimer laser light), and a difference in solubility rate in an alkaline developer occurs between the exposed area and the unexposed area due to reactions catalyzed by the acid. A resist pattern is formed on a substrate by utilizing the difference in solubility rate.
In order to form a finer resist pattern using the chemically-amplified resist, liquid immersion lithography that exposes the resist film in a state in which an immersion medium (e.g., purified water or fluorine-containing inert liquid) is provided between the lens and the resist film, has become widespread. According to liquid immersion lithography, the numerical aperture (NA) of the lens can be increased. Moreover, the depth of focus decreases to only a small extent, and high resolution can be obtained even when the NA of the lens is increased.
When forming a resist pattern by liquid immersion lithography, it has been desired to suppress elution of the resist film composition into the immersion medium, suppress pattern defects due to liquid droplets that remain on the surface of the film, and improve the scan speed. A technique that provides a protective film between the resist film and the immersion medium has been proposed to meet such requirements (see Patent Documents 1 to 3). In Patent Documents 1 to 3, a protective film is formed on the resist film using a water-insoluble and alkali-soluble polymer to suppress elution of the resist film composition, pattern defects, and the like during liquid immersion lithography due to the water repellency of the protective film. The protective film is removed from the surface of the resist film by dissolving the protective film in a developer in the subsequent alkali development step. Patent Documents 1 to 3 disclose using a structural unit that includes a sulfo group as a component of the polymer.
It is desirable that the upper layer film have excellent water repellency. However, the solubility of the upper layer film in a developer may decrease as a result of improving the water repellency of the upper layer film. In this case, the resist may show defects such as bridge defects (i.e., the lines of the pattern are partially connected) and blob defect (i.e., defects due to adhesion of a development residue).